Apparatus for testing the eyesight.



H. M. BLACK.

APPARATUS FOR TESTING THE EYESIGH'I.

APPLICATION FILED JUNE 30, 1911.

Patented Sept. 9, 1913.

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To all whom it may concern opticiam'of 16 New Steine, Brighton, Sus- ,seX, England, have invented new and useful Improvements Relating to Apparatus for Testing the Eyesight; and I. do hereby declare that the following is a full, clear and exact description of the same, reference being had to the accompanying drawings, forming a part hereof.

This invention has reference to apparatus for testing the eyesight and has for its object to provide improved means whereby the known means of testing the sight by the aid of an incomplete ring or line is utilized.

Recent research in ophthalmics has demonstrated that the most convenient stand ard test for vision is an incomplete ring of such size that from the eye of the observer the diameter ofthe ring subtends an angle of five minutes, the width of the ring subtending one minute and the interval in the ring being of the same width.

As is well known vision is measured by the distance by which two points must be separated to be distinguished as separate points as compared with their distance from the observer. This is the visual angle. The incomplete ring or line, the person tested being required to determine in which direction it is incomplete is an exact and extremely simple application of this principle and it is the object of my present invention to employ this principle in an improved manner.

lVith these ends in view my invention consists in providing a disk or plate with a ring or line inscribed thereon, the ring or line being either incomplete or rendered apparently incomplete by a movable interval, and in mounting the said disk or plate in such a manner that it may be rotated or moved against a dial or the like, hearing figures or signs of any description all as more particularly hereinafter described and finally pointed out in the claim.

In order that my invention may be readily'understood and carried into effect I will now proceed to describe the same fully for which purpose reference is' to be had to the accompanying drawings in which Figure 1 is an elevation of one form of device embodying my invention and Fig. 2 a view of the same with the dial removed. Fig. 3 is a section on line 11 of Fig. 1.

Specification of Letters Patent.

.Fig. 4 is a front view of the parts underlying the diaphragm and Fig.1 5- ;is; a rearview of the same. i

Referring to the form of the invention illustrated in Figs. 1 to 5 I provide a casing a which may conveniently be similar to a watch case. Within said casing a is mounted an iris diaphragm b in the casing a which is adapted to be rotated in casing a by means of the pinion 01 secured to and operated by the stem wind 0 to which end the casing 0 is provided with a toothed rim f gearing with said pinion in the position of the parts as shown in Fig. 3 so that upon turning the stem 6 the casing a will be turned within the casing a; for a purpose to be hereinafter explained. The blades of the iris diaphragm Z) which are white are arranged over a black background 9 and are opened or closed by depressing the stem 6 in such a .manner that the pinion 03 engages a toothed rim h (Fig. 3) when upon turning said stem 6 the blades of the iris diaphragm will open or close upon the Patented Septfi, 1913...

Application filed June so, 191 sens-1 no. 63 5 225. i

ring formed on the black background 9 to be varied. The break j in the ring is also varied in width in the following manner:

Mounted in the center of the casing is a pinion 70 (Fig. 4) to which an arm Z is rigidly secured the end of which engages with a stud secured to the rim f. Mounted on the iris diaphragm'and arranged to gear with said pinion k are two racks m m to which are secured two slides a n. It will thus be seen that as the blades of the iris diaphragm are operated to alter the width of the ring c' the slides 11, a will be operated to vary the width of the break in the ring when there is relative movement between the rims h and g. By engaging the pinion (Z with toothed rim f and turning the stem 6 the whole of the casing 0 will be rotated within the casing a the person whose acuteness of vision is being tested being required, to indicatein which direction I the ring is broken and to facilitate this thejdial 0 is provided with figures signs or letters as shown for example in Fig. 1.

, What I do claim as my invention and desire to receive by Letters Patent is An apparatus for testing eyesight comprising in combination, a casing, a circular support rotatively mounted in said casing and provided with a circular iris diaphragni and its support, said diaphragm means for varying the size of such interrupcomprising White blades and a black backtion substantially as described. 10 ground disposed behind said blades and In testimony whereof I aflix my signahaving a White center, mechanism adapted ture in presence of two witnesses.

for operation by said means for opening or HUGH MILNER BLACK. closing said blades to vary the size of the Witnesses:

black background to be disclosed, said dia- GEO. PRINGLE,

phragm having a radial interruption, and PERCIVAL HQCARTER.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents,

' Washington, D. G. 

